1. Field of the Invention
The present invention is directed generally to an emergency lighting system for supplying emergency power to a lighting device. More particularly, the present invention is directed to an emergency lighting system which selectively energizes a lighting device upon the occurrence of a power interruption and includes a branch circuit relay at the lighting panel comprising a plurality of relays for directing alternating current (AC) power to the branch circuit during normal operation, and direct current (DC) power to the branch circuit during emergency power operations. In addition, the system includes a time delay circuit in which, upon restoration of AC power to the branch circuit, allows line detection circuitry to stabilize before switching from an emergency mode to the normal mode.
2. Description of Related Art
Emergency lighting is utilized in buildings to provide light for egress and to direct occupants toward the exits in case of a loss of main power to a building. In related art systems, this is generally accomplished by installing exit and emergency lighting fixtures having self-contained batteries or battery powered inverters mounted internal to fluorescent lighting fixtures within these buildings. The self-contained exit and emergency lighting fixtures utilize small batteries which are kept charged in case of main power failure. In the case of the loss of main alternating current (AC) power, the self-contained exit fixture switches power from the lamps within the unit (which function off of main AC power) to a set of direct current (DC) powered lamps which are powered by an internal battery within the exit fixture. In a situation resulting in the loss of main AC power, the self-contained emergency light senses the loss of power and, in response thereto, energizes a set of DC powered lamps from the internal battery within the emergency light fixture. Internal battery powered inverters mounted within fluorescent fixtures operate similarly to self-contained batteries in that they also operate to sense a loss of main power and ignite and hold selected fluorescent lamps in response thereto.
There are several disadvantages to having these many independent battery operated fixtures throughout the buildings. For instance, because the emergency components operate in a very hostile environment as a result of being mounted within the fixture, they expose the batteries to undue heat. In addition, over time, because the batteries are maintained at a constant charge, they deteriorate in their ability to provide the rated output required by code to allow safe egress from the building in which they are installed. Furthermore, the required maintenance and testing of the fixtures is commonly ignored, and thus, the safety of the system is compromised. Additionally, leakage from the batteries commonly results in damage to both the fixtures and the surrounding environment.
Larger buildings are generally provided with emergency lighting devices which utilize central battery systems for powering exit and emergency fixtures. The central battery system is advantageous in that it can keep the batteries maintained at full charge, monitor the lifetime of the batteries, provide a single location for maintenance, and be equipped to alarm the building in the event of a sensed abnormal condition. The central battery system is disadvantageous in that it utilizes separate wiring for the main AC system and the emergency DC system. This redundancy adds obvious additional cost to new installations which may also be inconvenient to install. In addition, central battery systems are usually not an option for existing buildings which require the installation of a new emergency lighting system, and thus, requires the installation of new conduit and wiring dedicated to the emergency lighting system, which is often impractical due to costs or esthetic reasons.
In view of the foregoing, it is an object of the present invention to overcome obviate the disadvantages in the related art in providing an emergency lighting system which detects a power interruption in the main lighting system.
It is a second object of the present invention to provide an emergency lighting system which controls the operation of main and emergency lighting fixtures within a building or structure.
It is a third object of the present invention to provide an emergency lighting system which utilizes existing wiring for controlling the operation of main and emergency lighting fixtures.
It is a fourth object of the present invention to provide an emergency lighting system which automatically switches from the AC power source to a DC power source upon the detection of a power interruption in the main power source regardless of an on/off switch position of the light branch circuit.
It is a fifth object of the present invention to provide an emergency lighting system which stabilizes the lighting circuitry upon switching from emergency power to main power.
These and other objects are achieved in the present invention by providing an central battery emergency lighting system that allows the sharing of the main AC branch circuit wiring for both the main and emergency power distribution within a building or structure. The sharing of the branch circuit wiring is accomplished by introducing a branch circuit relay at the lighting panel connected to a DC central battery system. Accordingly, during circumstances in which the main AC voltage is not present due to an interruption in power (i.e., an outage or shortage), a line detection circuit detects the loss of the AC voltage and the branch circuit relay switches the line to thereby provide a source of emergency power to the branch circuit from the voltage from the DC central battery system. Additionally, line detection circuits are provided in the lighting fixtures for actuating and operating an emergency lamp. Upon detecting the loss of AC voltage, the line detection circuit automatically switches power to a dedicated emergency lamp within the lighting fixture. Upon the restoration of main power, the lighting fixture resets to the AC voltage lamps to allow the resumption of normal operations.
The central battery emergency lighting system also includes switch sensing to allow DC power to be transmitted to an emergency fixture regardless of the position of the main AC lighting switch position. The switch sensing allows for the main AC wiring of the lighting system with appropriate light switches within the building, and bypasses the switches during emergency DC operation regardless of the switch position. In addition, the system utilizes an automatic time delay circuit for delaying re-energizing the line with AC power to allow stabilization of the switch circuits between emergency and normal modes.
In accordance with an embodiment of the invention, the line detection circuits are installed in predetermined locations, and preferably, are located within any type of normal lighting fixture. For example, fluorescent lay-in lighting fixtures are equipped with a line detection circuit mounted within or adjacent to the ballast chamber to thereby direct main AC power to the fluorescent ballast and emergency backup power to the dedicated emergency lamps. In addition, the line detection circuits will actuate and hold the lamp in an emergency operation mode. For recessed incandescent lamps, the line detection circuits are modified for mounting within a junction box adjacent to the light fixture to direct the main AC power to the light fixture and the emergency DC power to an appropriate local emergency lighting fixture. Exit fixtures equipped with both AC and DC powered lamps may also be provided with a line detection circuit for directing power to the appropriate lamps.